The present invention relates to a method and a structure for restraining a vibration of a building.
Buildings and civil structures are induced to vibrate by earthquakes, winds, traffic, and other vibration sources. On the other hand, most of modern buildings and structures have more flexibility and less damping compared to conventional buildings by virtue of affluent flexibility in modern structural members and precise construction techniques. However, because modern buildings permit larger displacements than before, vibration in modern buildings tend to become larger than in conventional buildings. Then, excessive vibrations may occur and cause such various inconveniences and problems in the building as damage on nonstructural members of the building, misoperation of equipment installed in the building and uncomfortable feeling of motion by the occupants etc. Reduction of vibration is desirable for the structural members of the building also.
In order to resolve these inconveniences, present inventors already proposed a vibration restraining apparatus for buildings in a Japanese Patent Application 60-241045, FIG. 1. By the Patent Application, disclosed is a vibration restraining apparatus comprising a tank and a liquid retained in the tank to be installed at a roofing of the building. As the building vibrates, the vibrational energy of the building is transmitted to the liquid, and the liquid, having a sloshing natural frequency identical to that of the building, sloshes resonantly with the building. Consequently, the vibration of the building is restrained as loosing the vibrational energy. Weight of the liquid retained in the tank had better be larger than 1% of the building so as to restrain vibration of the building effectively.
A problem as to foregoing conventional apparatus and methods for restraining vibration of a building is that the apparatus requires a large space to be installed in and consequently the space to install the apparatus is found only at the top of the building.
Another problem in conventional apparatus and methods is that a number of such tanks have to be installed because the size of the liquid tank, which is relatively small in general, is determined in order to make the sloshing frequency thereof equal to that of the building and because liquid of 1% by weight of the building has to be retained in tanks in total.
A further problem is that the apparatus effectively restrains only the first mode of the building as a logical consequence, when the tanks are installed at the top of the building.